Alpha-olefins can be copolymerized with rigid cyclic olefins, such as ethylidene norbornene and dicyclopentadiene, using various polymerization catalysts. When these copolymers contain more than 30 wt. % cyclic olefins, they are typically amorphous and transparent (>90% light transmittance) and have glass transition temperatures above room temperature (>50° C.). With higher levels of cyclic olefin incorporation they have exceptionally high moduli (>2900 MPa), heat distortion temperatures (>130° C. @66 psi), and Rockwell hardness (>100). However, they have very poor notched Izod impact properties (<0.5 ft-lb/in @ room temperature) and have brittle failures in the instrumented impact test at room temperature and below (brittle failures are cracks that propagate without plastic deformation of the polymers).
Thus, without modification, cyclic olefin copolymers have too little impact resistance to be used in most structural applications, such as automotive components. To improve their impact resistance, cyclic olefin copolymers are therefore generally blended with various elastomers. However, when cyclic olefin copolymers are blended with elastomers, their flexural, tensile, and Young's moduli drop significantly. For automotive applications the ideal compounds would have good impact properties and good heat distortion temperatures, while maintaining as high as possible flexural, tensile, and Young's moduli. To accomplish these balanced properties, reinforcements are often added to toughened blends. To improve the effectiveness of the reinforcements, coupling agents, such as an epoxy resin also added in the blends.
Blending of cyclic olefin copolymers with elastomers is typically achieved by melt-mixing followed by extrusion. However, the high Tgs of the cyclic olefin copolymer materials (up to 160° C.) require that melt-mixing and extrusion be carried out at high temperatures (>230° C.). Thus to avoid degradation of both the base copolymer and the elastomer used as the impact modifier, it is necessary to minimize both the time and temperature of melt-mixing, yet still provide conditions that ensure good mixing between the base material and the elastomer. There is therefore significant interest in developing impact modification procedures that retain the advantageous properties of the starting polymers and avoid or minimize the need for melt mixing.
Copolymers of alpha-olefins with dienes contain residual unsaturation that can act as a “reactive hook” to allow functionalization of the copolymer. Functionalization of cyclic olefin copolymers via the residual unsaturation can increase the polarity and Tg of the copolymer and is also predicted to improve interactions with fillers. Functionalized polyolefin (FPO) materials have potential usefulness for a number of commercial applications. Polyolefins which are reactive or polar can, for example, provide products for major applications, such as high temperature elastomers resistant to oil, and can also provide structural polyolefins. Polyolefins in the form of oil resistant elastomers could compete with chloroprene and nitrile rubber in oil resistant applications but could offer better high temperature performance and service life than ethylene-propylene diene rubbers at a comparable price. Structural polyolefins could be low cost polymers with improved stiffness, strength and use temperatures that would extend the boundary of polyolefins to structural applications, for example to uses within the automotive area.
Thus, functionalization of polymers has joined copolymerization and blending as a common means of altering and optimizing the physical and mechanical properties of macromolecules. One known functionalization reaction is epoxidation, which is a stereospecific reaction in which diene polymers are reacted with an oxidizing agent such as performic acid or m-chloroperbenzoic acid. Such epoxidation reactions can provide quantitative or near-quantitative conversion of the residual diene co-monomer double bonds into oxirane groups.
For example, Marathe et al. in Macromolecules, Am. Chem. Soc., Vol. 27, pp. 1083-1086 (1994), disclose the synthesis of poly(ethylene-co-5-vinyl-2-norbornene) with the CP2ZrCl2 (Cp=cyclopentadienyl)-methylaluminoxane (MAO) catalyst system and the subsequent conversion of the vinyl groups in the resultant copolymer into the hydroxyl/epoxy groups. The functionalization is carried out using m-chloroperbenzoic acid as oxidizing agent.
In addition, Sarazin et al. in Macromol. Rapid Commun., Vol. 26, pp. 1208-1213 (2005), disclose the copolymerization of propylene with 5-vinyl-2-norbornene (VNB). The copolymers are then converted into polar polymers via functionalization of the pendant vinyl side chains. For example, the P/VNB copolymer can be reacted with m-chloroperbenzoic acid in hot toluene to produce the epoxy-functionalized copolymer. This reference also shows reaction of the P/VNB copolymer with ozone in chloroform followed by PPH3 and MEOH/HCl to produce an ester functionalized copolymer.
Japanese Published Patent Application No. JP2001-031716A, published Feb. 26, 2001, discloses the synthesis of epoxy-ethylenedicyclopentadiene (E/DCPD) copolymers having 16, 27, and 40 mole % epoxy-DCPD units and Tgs of, respectively, 56, 112, and 178° C. These materials are derived from E/DCPDs synthesized using a μ-(CH2CH2)bis(1-indenyl)ZrCl2 catalyst and having GPC molecular weights of Mw≦150,000 (versus polystyrene standards). The exemplified epoxidation of the copolymer is carried out in a toluene solvent using a premixed combination of formic acid and hydrogen peroxide as an epoxidizing agent. IR and NMR analysis of the resulting epoxidized copolymer is said to show that 100 mol % of the unsaturated bonds in the copolymer are converted to epoxy groups.
Epoxide functionalization of elastomeric copolymers is also known. For example, Song et al. in J. Polym. Sci. Part A: Polym. Chem., Vol. 40, pp. 1484-1497 (2002) disclose the copolymerization of propylene with 7-methyl-1,6-octadiene, followed by chemical modification of the residual double bonds to obtain polar functionalized polyolefins. The article discusses several functionalization chemistries that include m-chloroperbenzoic acid-based epoxidation, reduction to alcohols, ozonolysis, etc.
Although epoxide functionalization can be conducted in the absence of a catalyst, the use of an epoxidation catalyst can eliminate the need for the presence of large amounts of acidic reagents and can permit the use of a hydrogen peroxide oxidizing agent. But the presence of a catalyst can also promote crosslinking or side reactions of the diene-containing copolymer and/or can also potentially degrade the hydrogen peroxide oxidizing agent which is being used along with the catalyst. Rhenium-containing catalysts have been used to epoxidize and/or hydroxylate a variety of non-polymeric alkenes. And there are a few examples in the art of catalytic oxidation being used to introduce epoxy groups into copolymers containing relatively low levels of unsaturation or unsaturation which is primarily found within the copolymer backbone.
For example, Herrmann et al. in Angew. Chem. Int. Ed. Engl., Vol. 30, No. 12, 1638-1641 (1991), disclose the use of methyltrioxorhenium to catalyze epoxidation of non-polymeric alkenes with hydrogen peroxide. Alkanol reaction solvents are used for such epoxidation. Similarly, U.S. Pat. No. 5,155,247 discloses the use of ligand-bound alkyltrioxorhenium to catalyze the oxidation of non-polymeric olefinic compounds to epoxides or diols using hydrogen peroxide. Olefinic compounds oxidized include cyclooctadiene, squalene, methyl oleate, 3-methyl-1,2-butadiene, styrene and styrene derivatives.
Van Vliet et al. in Chem Commun, pp. 821-822 (1999), disclose methyltrioxorhenium-catalyzed epoxidation of non-polymeric, substituted and unsubstituted alkenes using hydrogen peroxide in a trifluoroethanol solvent. Alkenes such as C6-C10 alkenes, vinylcyclohexene, styrene, phenylpropene and phenylbutene are exemplified.
Moreover, in SYNLETT, 2004, No. 10, pp. 1849-1850 (2004), Soldaini reviews the literature relating to the use of methyltrioxorhenium (MTO) to catalyze oxidation of various compounds using hydrogen peroxide. MTO catalyzed epoxidation of non-polymeric alkenes is disclosed as are epoxidation processes which utilize small amounts of pyridine or pyridine derivatives to prevent epoxidized alkenes from being converted to corresponding diols.
Although the preceding discussion demonstrates that epoxidation has been widely used to functionalize olefins and olefin polymers, it is believed that epoxidation and/or hydroxylation has to date never been suggested as a route for effecting in-situ functionalization and impact modification of a rigid cyclic diene copolymer, such as E/DCPD, in admixture with a flexible or elastomeric copolymers derived from dienes such as 7-methyl-1,6-octadiene (MOD), 4-vinyl-1-cyclohexene (VCH), and 1,4-hexadiene. The in-situ epoxidation can be conducted on a solution of the rigid and elastomeric copolymers, thereby resulting in co-precipitation of the epoxidized (and possibly also hydroxylated) products and hence avoiding the need for the melt mixing conventionally used to effect impact modification of cyclic olefin copolymers. Moreover, the resultant epoxidized material typically retains the high and low Tg values associated with the rigid and elastomeric precursors respectively. In addition, the process can be selectively controlled in such a way that the rigid cyclic olefin copolymer, such as E/DCPD, forms an epoxide, while the flexible elastomer, such as an ethylene-propylene-diene monomer (EPDM) copolymer rubber, forms epoxide ring opened products, such as diols or copolymers with both hydroxyl and ester groups.